This is the equation of a straight line. When the line crosses the x-axis that is the x- intercept, the corresponding y-coordinate will be zero. Substituting y = 0 into the equation and solving for x gives the x-intercept.
8x-(4×0)=-64
-8x=-64
x=8 <= the x-intercept.
Similarly, when the line crosses the y-axis the corresponding x- coordinate will be zero. Let x = 0 and solve for y.
This is just an assumption considering that there are more red than blue but only trumps blue by 2. Taking out those two, you’d be left with a 50% chance of getting red and/or blue marbles